Simulation study of drilling fluid cooling in long horizontal wells based on phase change heat absorption

ABSTRACT

The shale gas resources found in deep formations are abundant and represent a crucial area for current and future shale gas development. However, as shale gas exploration and development intensify in China, an increasing number of high-temperature formations are being encountered during drilling, presenting significant challenges to drilling engineering and severely constraining the development of deep shale gas exploration. In this study, the stability of PCM (phase change material) combined with drilling fluid as a coolant was discussed, and the influence of PCM on wellbore temperature field in drilling fluid was considered. A calculation model of temperature field of drilling fluid containing PCM was established, the cooling characteristics of PCM under the influence of different parameters were simulated, and the cooling effect of PCM integrated with drilling fluid on ultra-deep and high-temperature Wells was analyzed. The investigated PCM has a phase change temperature range of 120 ~ 130°C and a latent heat of 264.15 ~ 265.53 kJ/kg. Our results showed that the cooling impact of PCM exhibits an upward trend as the quantity of PCM utilized increases. Assuming the drilling temperature limit is 135°C, after adding 5% PCM to the drilling fluid, the drilling length of the horizontal section increased by approximately 500 m. With 15% PCM added, the horizontal section could be extended by about 1000 m. We conducted a simulation analysis on a well in southern Sichuan, and found that adding 12% PCM had the best cooling effect, reducing the bottom hole temperature by 12.3°C and extending the horizontal section by 700 m. Compared with conventional drilling fluid cooling methods, incorporating PCM as cooling agents within the drilling fluids provided better cooling effects. It effectively addressed the problem of excessive bottom-hole temperatures in deep wells, extended the drilling length of horizontal sections, and prolonged the service life of downhole instruments. Our research lays the groundwork for the future investigation of cooling techniques for high-temperature deep well drilling fluids.

KEYWORDS:

• Drilling fluid
• temperature distribution
• PCM (phase change material)
• long horizontal wells
• high temperature well cooling

Nomenclature

$c$	=	specific heat capacity, J/(kg·℃)
$t$	=	time, s
$z$	=	well depth, m
$h$	=	Convective heat transfer coefficient, W/(m2·℃)
L	=	latent heat of phase transition, kJ/kg
$q$	=	volume flow rate of drilling fluid, m3/s
$Q_m$	=	internal heat source, W/m3
$Q_a$	=	heat source inside the drill string, W/m3
$r$	=	radius, m
$T$	=	temperature,°C
$T_m$	=	phase transition temperature,°C
$\mathrm{\Delta }T$	=	Phase transition temperature interval,°C
Greek Symbols	=
$\lambda$	=	thermal conductivity, W/(m·℃)
$\rho$	=	density, kg/m3
Subscripts	=
0.1.2.3.4.i	=	regions of fluid in drill string, drill string wall, fluid in annulus, borehole wall and formation, respectively
$i$	=	i th layer in the radial direction
$j$	=	j th layer in the axial direction
$g$	=	before phase transformation
${ }_f$	=	at phase transition
$y$	=	after phase transformation
$z$	=	at $z$ position

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this paper.

Additional information

Notes on contributors

Jie Zhang

Jie Zhang is currently a professor in the Department of Petroleum and Natural Gas at Southwest Petroleum University in China. In 2005, he graduated from Southwest Petroleum Institute with a PhD in Oil and Gas Well Engineering. Jie Zhang's interestsinclude multiphase-flow modeling, heat and mass transfer, drilling oil and gas well, and refrigeration.

Jiaohao Xie

Jiaohao Xie is currently a master's candidate in the Department of Petroleum and Natural Gas, Southwest Petroleum University, China. His main focus is on drilling multi-phase flow, heat and mass transfer, and high-temperature drilling.

Xin Li

Xin Li is currently a Ph.D candidate at Petroleum Engineering School of Southwest Petroleum University, Chengdu, Sichuan, China. He holds a master degree in petroleum engineering from Southwest Petroleum University in China since 2020. He is very active in petroleum engineering research and has published many research articles from petroleum engineering. Xin's interest include wellbore fluid mechanics and pressure control, wellbore heat transfer and temperature control, as well as wellbore damage mechanics and abandoned well renovation.